Fractionalized Fermi liquid in square-lattice Kondo-Heisenberg model

The Kondo-Heisenberg model on a (unfrustrated ) square lattice is studied via a controlled large-$N$ [Sp(2N)] approach to demonstrate on a general ground the existence of a peculiar metallic state so-called "fractionalized Fermi liquid (FL$^*$)" with unbroken translational symmetry and a Fermi surface volume not controlled by the total electron density. Close to half-filling, we show that the nesting of Fermi surface favors the Kondo hybridization to form between conduction electrons and local resonant-valence-bond spin-liquid fermions, which stabilizes FL$^*$ state with well-defined quasi-particle and gapped spinon excitations. Our result generalizes the FL$^*$ state previously proposed in Phys. Rev. Lett. 90, 216403 (2003), which is restricted to frustrated Kondo lattice systems.

This work is supported by the MOST Grant NO. 107-2112-M-009-010-MY3, the NCTS of Taiwan, R.O.C. (C.-H. C.), Office of Basic Energy Sciences, Material Sciences and Engineering Division, U.S. Department of Energy (DOE) under Contract No. DE-SC0012704 (A.M.T.).